Method for managing a trusted identity

ABSTRACT

The invention is a method for deploying a trusted identity for a user issued by an issuer. The user has a user device configured to send a request for signature to an issuer device handled by the issuer. The request comprises a user public key allocated to the user. The issuer device is configured to compute an issuer signature by signing both the user&#39;s trusted identity and the user public key using an issuer private key allocated to the issuer. A block chain transaction containing the issuer signature is created and submitted to a Block Chain for transaction verification and storage.

FIELD OF THE INVENTION

The present invention relates to methods of managing a trusted identityfor a user. It relates particularly to methods of deploying user'strusted identity and to methods of authenticating user's trustedidentity.

BACKGROUND OF THE INVENTION

Centrally issued and trusted identities are widely used for employment,tax, mortgage, health care or social security benefits for example. Atrusted identity is an identity whose content can be authenticated.However, identity theft and identity fraud are major problems. Each yearfraudsters stole billions of dollars from millions of consumers. Such afraud is possible because there is no easy way to verify the true ownerof a trusted identity. In other words, a thief can use a stolen trustedidentity since only the validity—as such—of the trusted identity iscontrolled.

Therefore, there is a need to develop new methods and devices allowingto prevent several people from claiming a same trusted identity.

SUMMARY OF THE INVENTION

An object of the invention is to solve the above mentioned technicalproblem.

An object of the present invention is a method for deploying a trustedidentity for a user issued by an issuer. The user has a user deviceconfigured to send a request for signature to an issuer device handledby the issuer. The request comprises a user public key allocated to theuser. The issuer device is configured to compute an issuer signature bysigning both the user's trusted identity and the user public key usingan issuer private key allocated to the issuer. A block chain transactioncontaining the issuer signature is created and submitted to a BlockChain for transaction verification and storage.

Advantageously, the issuer device may send the issuer signature inresponse to the request and the block chain transaction may be createdby the user device and may contain the user's trusted identity.

Advantageously, the user device may generate an encrypted identity byencrypting the user's trusted identity with a secret key generated inthe user device. The user device may generate an encrypted key byencrypting the secret key using a key encryption key. The block chaintransaction created by the user device may contain the encrypted key andthe encrypted identity.

Advantageously, the key encryption key may be a public key belonging toa key pair generated by the user device.

Advantageously, the request may comprise a block chain address. Theissuer device may generate an encrypted identity by encrypting thetrusted identity with a secret key generated in the issuer device. Theissuer device may generate an encrypted key by encrypting the secret keyusing the user public key. The issuer device may create a block chaintransaction containing a digital asset including both the issuersignature, the encrypted identity and the encrypted key and may submitthe block chain transaction to the Block Chain for transactionverification and storage to the block chain address.

Advantageously, the request may comprise a block chain address. Theissuer device may compute a hash of the trusted identity and send thetrusted identity to the user device. The issuer device may create theblock chain transaction containing the hash and submit the block chaintransaction to the block chain for transaction verification and storageto the block chain address. The user device may receive the block chaintransaction from the block chain.

Another object of the present invention is a method for authenticating auser trusted identity by a verifier device. The user trusted identity isbeing issued by an issuer. The user has a user device which sends amessage to the verifier device. The message comprises a transactionidentifier and a user public key allocated to the user. The verifierdevice retrieves a block chain transaction comprising an issuersignature from a block chain using the transaction identifier andverifies the transaction. In case of successful verification, theverifier device sends a challenge to the user device which computes aresponse by signing the challenge using the user's private key and sendsthe response to the verifier device. The verifier device checks the usersignature using the user public key and, in case of successful checking,the verifier device verifies the issuer signature using the user trustedidentity, the user public key and the issuer public key.

Advantageously, the verifier device may retrieve the user trustedidentity from a block chain transaction or may receive the user trustedidentity from the user device.

Advantageously, the block chain transaction may contain an encrypted keyand an encrypted identity. In case of successful checking of the usersignature, the verifier device may send the encrypted key and a verifierpublic key to the user device. The user device may derive a keyencryption key and retrieve a secret key by decrypting the encrypted keyusing the key encryption key. Then the user device may encrypt thesecret key using the verifier public key and send the resulting newencrypted key to the verifier device. The verifier device may retrievethe secret key by decrypting the new encrypted key using a verifierprivate key, then the verifier device may retrieve the user trustedidentity by decrypting the encrypted identity using the secret key.

Another object of the present invention is a user device configured toreceive a user trusted identity generated by an issuer device and tosend a request for signature to the issuer device. The request comprisesa user public key allocated to a user of the user device. The userdevice is configured to receive, in response to the request, an issuersignature generated by signing both the user trusted identity and theuser public key using an issuer private key allocated to the issuer. Theuser device is configured to create a block chain transaction containingthe issuer signature and to submit said block chain transaction to aBlock Chain for verification and storage.

Advantageously, the user device may be configured to generate anencrypted identity by encrypting the user's trusted identity with asecret key generated in the user device. The user device may beconfigured to generate an encrypted key by encrypting the secret keyusing a key encryption key. The user device may be configured to includethe encrypted key and the encrypted identity in the block chaintransaction.

Advantageously, the user device may be configured to send a message to averifier device, said message comprising a transaction identifier and auser public key allocated to the user. The user device may be configuredto compute a response by signing a challenge received from the verifierdevice using the user's private key and to send the response to theverifier device.

Another object of the present invention is an issuer device configuredto send a trusted identity for a user. The trusted identity is issued byan issuer. The issuer device is configured to receive a request forsignature from a user device, said request comprising both a block chainaddress and a user public key allocated to the user of the user device.The issuer device is configured to compute an issuer signature bysigning both the user's trusted identity and the user public key usingan issuer private key allocated to the issuer. The issuer device isconfigured to generate an encrypted identity by encrypting the trustedidentity with a secret key generated in the issuer device. The issuerdevice is configured to generate an encrypted key by encrypting thesecret key using the user public key. The issuer device is configured tocreate a block chain transaction containing a digital asset includingthe issuer signature, the encrypted identity and the encrypted key andto submit the block chain transaction to a Block Chain for transactionverification and storage to the block chain address.

Another object of the present invention is an issuer device configuredto send a trusted identity for a user issued by an issuer. The issuerdevice is configured to receive a request for signature from a userdevice, said request comprising both a block chain address and a userpublic key allocated to the user of the user device. The issuer deviceis configured to compute an issuer signature by signing both the user'strusted identity and the user public key using an issuer private keyallocated to the issuer. The issuer device is configured to generate ahash of the trusted identity. The issuer device is configured to sendthe trusted identity to the user device. The issuer device is configuredto create a block chain transaction containing the hash and to submitthe block chain transaction to a Block Chain for transactionverification and storage to the block chain address.

Another object of the present invention is a verifier device configuredto authenticate a user trusted identity of a user issued by an issuerhaving a public key. The verifier device is configured to receive amessage from a user device of the user, said message comprising atransaction identifier and a user public key allocated to the user. Theverifier device is configured to retrieve a block chain transactioncomprising an issuer signature from a block chain using the transactionidentifier and to verify the transaction. In case of successfulverification, the verifier device is configured to send a challenge tothe user device, to get a response computed by the user device and tochecks the response using the user public key. In case of successfulchecking, the verifier device is configured to verify the issuersignature using the user trusted identity, the user public key and theissuer public key.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention willemerge more clearly from a reading of the following description of anumber of preferred embodiments of the invention with reference to thecorresponding accompanying drawings in which:

FIG. 1 depicts a flowchart showing a first example of identity issuancesequence according to the invention,

FIG. 2 depicts a flowchart showing an example of identity proofingsequence according to the invention,

FIG. 3 depicts a flowchart showing a second example of identity issuancesequence according to the invention,

FIG. 4 shows an example of an issuer device according to the invention,

FIG. 5 shows an example of a user device according to the invention, and

FIG. 6 shows an example of a verifier device according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention may apply to any type of digital identity issued by anissuance authority (also called issuer) and intended to be allocated toa user.

The invention relies on public/private key pair and cryptographicfunctions as commonly used in the so-called public-key cryptographydomain.

The user is supposed to have a device (called user device) which is usedfor the trusted identity deployment and for the trusted identitychecking. The user device may be a passport, a driving license, a smartphone, a tablet PC, an electronic pair of glasses, an electronic watch,an electronic bracelet, an electronic wearable device, a portable gamingmachine or a computer for example.

Identity issuer is the entity who issues the trusted identity, e.g.driver license, social security number, passport, health care ID, etc.Thus the trusted identity can be an identity document issued by anissuer and may contain an identifier, various information, or userattributes. The trusted identity can also be one or more vettedattributes associated with a user. In this case, the issuer vouches forthe attributes.

The user is assumed to request for a trusted identity (or vouch ofattributes) and to use the trusted identity when needed. The user can bea person, a machine, or an Internet of Thing (IoT).

The verifier is an entity who needs the user to prove the ownership andlegitimacy of the trusted identity. For example, a verifier can be aservice provider, e.g. a bank, or a peer to the user, e.g. another IoT.The user is assumed to want a service from the service provider, e.g.apply for a mortgage. The service provider wants trusted identity fromthe user and needs to know that the user is indeed the owner of thetrusted identity. The user needs to prove it. The verifier is assumed toknow and trust the issuer.

A block chain (also named blockchain) is a distributed ledger whichmaintains a continuously growing list of transactional data recordsassumed to be resistant against tampering and revision. Generally ablock chain relies on a timestamp server which, after batching recenttransactions into blocks, takes a hash of a block to be time stamped andwidely publishes the hash. The hash allows to prove that the data musthave existed at the time. The hash of each block includes the hash ofprior block. Thus a chain of blocks is created where each block linkedto its predecessor. Thus a transaction recorded in a block can be getfrom a block chain and it is possible to check that this recordedtransaction has not been altered. A block chain can be considered anincontestable record keeper. Additionally, a block chain can provideintegrity protection and pseudo-anonymity. One of the most widely knownapplication of the block chain technology is the public ledger oftransactions for the crypto currency bitcoin which aims at storingfinancial transactions.

For the sake of brevity, in the present specification, the word “user”is sometime used instead of “user device”. Similarly “issuer” issometime used instead of “issuer device” and “verifier” instead of“verifier device”.

FIG. 1 illustrates a first example of sequence for an identity issuanceaccording to the invention. In this example, the issuer is assumed tomanage an issuer device which may be an identity server able to generatetrusted identities and the user is a person assumed to manage a userdevice which may be a laptop.

The user device is able to communicate with the identity server (issuerdevice) through any kind of network. For instance, the communication maybe set through a combination of a wireless channel (like Wi-Fi® orBluetooth®) and a wired channel (like Ethernet).

First, the user (or user device) asks the identity issuer (or issuerdevice) for a trusted identity ID. The user provides necessary documents(e.g. birth certificate and optionally biometrics) that prove his/heridentity.

Then the issuer verifies the documents. If all is good, the issuercreates a new trusted identity ID and sent it to the user for safekeeping.

According to the invention, the user chooses to have a public record(i.e. a record in a public ledger): the user sends a request forsignature to the issuer. This request contains the public key Kpu of theuser.

Then the issuer digitally signs the couple trusted identity and userpublic key (ID|Kpu) and gives the resulting signature (i.e. issuersignature) to the user.

At this point, the user may directly create a block chain transactioncontaining the issuer signature.

Alternatively, the user may use a secret key K to encrypt the trustedidentity ID, to generate an encrypted trusted identity (e_ID). Then theuser may get a key encryption key (i.e. KEK). For instance, it mayderives a key (or key pair) KEK from a public/private key pair. Thederivation parameter can be handled in a number of ways. Then the userencrypts the secret key K using the key encryption key KEK (public keyif it is a key pair), resulting encrypted key e_K. At this stage, theuser creates a block chain transaction T containing a blob including theissuer signature, the encrypted trusted identity e_ID, and the encryptedsecret key e_K.

In both cases, the user submits the transaction to a block chain. Oncethe transaction T is verified (by the entity managing the block chain),the transaction T is recorded in the Block Chain.

In one embodiment, the invention may be implemented by using the formatof Bitcoin transaction if the block chain is a Bitcoin block chain. Inthis case, multiple output addresses are made of the data blob. Anotheroutput address can be the user's address. New transaction formats mayalso be defined for easy recording of digital assets.

FIG. 2 illustrates an example of identity proofing sequence according tothe invention.

In this example, a block chain transaction is assumed to have beencreated and recorded according to the invention.

The verifier is assumed to manage a verifier device which is able toaccess the block chain and interact with the user device. The verifierdevice may be a server connected to the Internet for instance.

In this example, the user wants to use some service provided by theverifier or wants to interact with the verifier in general. The verifierneeds user's identity ID. It wants verify that the trusted identity IDis indeed issued by an issuing authority and wants the user to provethat the trusted identity ID is indeed issued to him/her.

First, the user (or user device) tells the verifier his block chaintransaction identifier Id (or an identifier that can identify the user'stransaction or record), and a reference allowing to identify the issuerof the trusted identity ID. Additionally, the user may also provide theverifier with its public key Kpu.

Using the transaction identifier Id, the verifier finds the transactionT from the block chain and verifies the transaction T. In other words,the verifier check the genuineness and integrity of the recordedtransaction. If the transaction T is successfully checked, the verifiercontinues as follows.

The verifier verifies the user, indeed the owner of this transaction, bysending a challenge C. In response, the user signs the challenge C usinghis private key Kpr and sends back the result to the verifier. Theverifier verifies the received user's signature. In case of successfulverification, the verifier continues as follows.

If the data is encrypted, the verifier sends the encrypted key e_K(found in the transaction) and its own public key V_Kpub to the user.

Then the user re-encrypts the secret key K with the verifier's publickey V_Kpub resulting a new encrypted key V_e_K and sends it to theverifier. For instance, the user decrypts the encrypted key e_K usingthe key KEK and retrieves the secret K, and then re-encrypts the secretkey K with the verifier's public key V_Kpub. In this case, the user canthen delete the secret key K.

Then the verifier decrypts the new encrypted key V_e_K with its privatekey and retrieves the secret key. The verifier can now decrypts theencrypted identity e_ID using the secret key K and retrieves the trustedidentity ID.

The verifier verifies the Issuer's signature using User's ID, the user'spublic key Kpu and the issuer's public key. If the verificationsucceeds, the verifier can provide service to the user.

By the end, the verifier has verified that the issuer has indeed issuedthe trusted identity ID to the user who has the private keycorresponding to the user's public key.

Thanks to the invention, the verifier can check the user's trustedidentity without contacting the original issuer.

Alternatively, the user may keep the trusted identity ID instead ofputting it in the block chain transaction. In this case, the userpresents the trusted identity ID to the verifier and the verifier checksthe block chain record to verify that the trusted identity ID belongs tothe user.

In one example, the user's key pair is the same as the key pairassociated with the block chain address.

In another example, the user's key pair is different from thatassociated with the block chain address.

FIG. 3 illustrates a second example of sequence for an identity issuanceaccording to the invention.

The first steps are similar to those described at FIG. 1.

The user chooses to have a public record: the user device sends arequest for signature to the issuer device. This request contains boththe public key (Kpu4Id) of the user and a block chain address.

Then the issuer digitally signs the couple trusted identity and receiveduser public key (ID|Kpu4Id) to generate an issuer signature.

The issuer device generates an encrypted identity e_ID by encrypting thetrusted identity ID with a secret key K generated in the issuer device.The issuer device also generates an encrypted key e_K by encrypting thesecret key K using the received user public key (Kpu4Id).

Then the issuer device creates a block chain transaction T containing adigital asset including the generated issuer signature, the encryptedidentity e_ID and the encrypted key e_K. The issuer device submits theblock chain transaction T to the Block Chain for transactionverification and storage to the block chain address provided by theuser.

Instead of fully encrypting the trusted identity ID, the trustedidentity ID may also be partially encrypted. For example, the identifiermay be in clear while the attributes are encrypted.

In another embodiment (not shown), the ID issuer gives an (digital)identity document to the user, computes a cryptographic hash of thetrusted identity ID, and transfers the computed hash of the ID to theuser through the block chain as a digital asset.

For example, on receipt of the request comprising both the user's publickey and a block chain address, the issuer device computes a hash of thetrusted identity ID. The issuer device sends the trusted identity ID tothe user device and creates a block chain transaction T containing thehash. Then the issuer device submits this block chain transaction T tothe block chain for transaction verification and storage to the blockchain address of the user. Then the user device can receive the blockchain transaction T from the block chain.

The block chain in this invention can be a public block chain used formore than one purposes, or a private block chain serving identity andassociated purposes. It is to be noted that one or more identity issuersmay use the same block chain.

FIG. 4 illustrates schematically an example of an issuer deviceaccording to the invention.

The issuer device may be a server comprising a generator agentconfigured to generate a trusted identity for a user. The issuer devicecomprises a signature agent configured to receive a request forsignature comprising both a block chain address and a public keyallocated to the user. The signature agent is configured to compute anissuer signature by signing both the user's trusted identity and theuser's public key using an issuer private key allocated to the issuer.The issuer device comprises a hash agent configured to compute a hash ofthe trusted identity. For instance, the hash agent may implement theSHA-2 algorithms (Secure Hash Algorithms defined by the NationalSecurity Agency). The issuer device comprises a transaction agentconfigured to create a block chain transaction T containing a digitalasset which includes the issuer signature and the hash. The transactionagent is configured to submit this block chain transaction to a BlockChain for transaction verification and storage to the block chainaddress of the user.

In another example (not shown), the issuer device may comprise agenerator agent and a signature agent as described above. In addition,the issuer device may comprise a key generator adapted to generate asecret key and a ciphering agent configured to generate an encryptedidentity by encrypting the trusted identity with the generated secretkey. The issuer device comprises a transaction agent configured tocreate a block chain transaction containing a digital asset includingthe issuer signature, the encrypted identity and the encrypted key. Thetransaction agent is also configured to submit the block chaintransaction to a Block Chain for transaction verification and storage tothe block chain address.

FIG. 5 illustrates schematically an example of a user device accordingto the invention.

The user device may be a smartphone comprising a request agentconfigured to build a request for signature comprising the public key ofthe user of the user device and to send the request to an issuer device.The user device comprises a transaction agent configured to receive, inresponse to the request, an issuer signature generated by signing boththe user trusted identity and the user public key using a private keyallocated to the issuer. The transaction agent is also configured tocreate a block chain transaction containing the issuer signature and tosubmit this block chain transaction to a Block Chain for verificationand storage.

In another example (not shown), the user device may comprise a requestagent similar to the one described above and a ciphering agentconfigured to generate a secret key and to generate an encryptedidentity by encrypting the received user's trusted identity with thegenerated secret key. The ciphering agent is also configured to generatean encrypted key e_K by encrypting the secret key K using a keyencryption key. The ciphering agent is configured to identify the keyencryption key to be used. For instance, it can derive the KEK from asecret key, which it keeps.

Preferably, the user device may comprise a sender agent (not shown)configured to send a message to a verifier device, the messagecomprising a transaction identifier Id and a user public key Kpuallocated to the user. The user device may also comprise a crypto agentconfigured to compute a response by signing a challenge C received froma verifier device using the user's private key Kpr and to send theresponse to the verifier device.

FIG. 6 illustrates schematically an example of a verifier deviceaccording to the invention.

The verifier device may be a server comprising a block chain accessagent configured to receive from a user device a message comprising atransaction identifier Id and a user public key Kpu allocated to theuser of the user device, and to retrieve a block chain transaction(comprising an issuer signature) from a block chain using thetransaction identifier Id.

The verifier device comprises a Transaction verifier agent configured toverify (genuineness/integrity) the retrieved block chain transaction.

The verifier device comprises a Manager agent configured to, in case ofsuccessful transaction verification, send a challenge C to the userdevice and to get a response computed by the user device.

The verifier device comprises a Checking agent configured to check theresponse using the user public key (Kpu).

The verifier device comprises a Signature verifier agent configured to,in case of successful response checking, verify the issuer signatureusing the user trusted identity, the user public key and the issuerpublic key.

Alternatively, the verifier device may be configured to retrieve a hashfrom a block chain transaction and to verify if this hash is compatiblewith the trusted identity.

Optionally, the verifier device may be configured to receive the trustedidentity directly from the user device.

The agents of the issuer device, user device and verifier device may beimplemented as software components. Preferably, some cryptographicfeatures may be performed by hardware components.

Thanks to the invention, only the trust owner can prove the ownership ofthe trusted identity. A theft cannot prove the ownership because he doesnot have the private key.

The verifier can verify the owner and trustworthiness of a trustedidentity or attributes.

It must be understood, within the scope of the invention that theabove-described embodiments are provided as non-limitative examples.Features of the described examples may be partly and fully combined.

The invention claimed is:
 1. A method for deploying a trusted identityof a user issued by an issuer, wherein the user has a user deviceconfigured to send a request for signature to an issuer device handledby the issuer, said request comprising a user public key allocated tothe user, wherein, in response to receiving the request for signature,the issuer device is configured to compute an issuer signature bysigning both the user's trusted identity and the user public key usingan issuer private key allocated to the issuer, and wherein a block chaintransaction containing the issuer signature is created and submitted toa Block Chain for transaction verification and storage.
 2. The methodaccording to claim 1, wherein said issuer device sends the issuersignature in response to the request and wherein the block chaintransaction is created by the user device and contains the user'strusted identity.
 3. The method according to claim 2, wherein the userdevice generates an encrypted identity by encrypting the user's trustedidentity with a secret key generated in the user device, wherein theuser device generates an encrypted key by encrypting the secret keyusing a key encryption key, and wherein the block chain transactioncreated by the user device contains the encrypted key and the encryptedidentity.
 4. The method according to claim 3, wherein the key encryptionkey is a public key belonging to a key pair generated by the userdevice.
 5. The method according to claim 1, wherein said requestcomprises a block chain address, wherein the issuer device generates anencrypted identity by encrypting the trusted identity with a secret keygenerated in the issuer device, wherein the issuer device generates anencrypted key by encrypting the secret key using the user public key,and wherein the issuer device creates a block chain transactioncontaining a digital asset including both the issuer signature, theencrypted identity and the encrypted key and submits the block chaintransaction to the Block Chain for transaction verification and storageto the block chain address.
 6. The method according to claim 1, whereinsaid request comprises a block chain address, wherein the issuer devicecomputes a hash of the trusted identity and sends the trusted identityto the user device, wherein the issuer device creates the block chaintransaction containing the hash and submits said block chain transactionto the block chain for transaction verification and storage to the blockchain address, and wherein the user device receives the block chaintransaction from the block chain.
 7. A user device comprising aprocessing device and a memory, wherein the user device, via theprocessing device and the memory, is configured to receive a usertrusted identity generated by an issuer device and to send a request forsignature to the issuer device, said request comprising a user publickey allocated to a user of the user device, wherein the user device isconfigured to receive, in response to the request, an issuer signaturegenerated by signing both the user trusted identity and the user publickey using an issuer private key allocated to the issuer and wherein theuser device is configured to create a block chain transaction containingthe issuer signature and to submit said block chain transaction to aBlock Chain for verification and storage.
 8. The user device accordingto claim 7, wherein the user device is configured to generate anencrypted identity by encrypting the user's trusted identity with asecret key generated in the user device, wherein the user device isconfigured to generate an encrypted key by encrypting the secret keyusing a key encryption key, and wherein the user device is configured toinclude the encrypted key and the encrypted identity in the block chaintransaction.
 9. The user device according to claim 7, wherein the userdevice is configured to send a message to a verifier device, saidmessage comprising a transaction identifier and a user public keyallocated to the user, and wherein the user device is configured tocompute a response by signing a challenge received from the verifierdevice using the user's private key and to send the response to theverifier device.
 10. An issuer device comprising a processing device anda memory, wherein the issuer device, via the processing device and thememory, is configured to send a trusted identity for a user issued by anissuer, Wherein the issuer device is configured to receive a request forsignature from a user device, said request comprising both a block chainaddress and a user public key allocated to the user of the user device,wherein, in response to receiving the request for signature, the issuerdevice is configured to compute an issuer signature by signing both theuser's trusted identity and the user public key using an issuer privatekey allocated to the issuer, wherein the issuer device is configured togenerate an encrypted identity by encrypting the trusted identity with asecret key generated in the issuer device, wherein the issuer device isconfigured to generate an encrypted key by encrypting the secret keyusing the user public key, and wherein the issuer device is configuredto create a block chain transaction containing a digital asset includingboth the issuer signature, the encrypted identity and the encrypted keyand to submit the block chain transaction to a Block Chain fortransaction verification and storage to the block chain address.
 11. Anissuer device comprising a processing device and a memory, wherein theissuer device, via the processing device and the memory, is configuredto send a trusted identity for a user issued by an issuer, wherein theissuer device is configured to receive a request for signature from auser device, said request comprising both a block chain address and auser public key allocated to the user of the user device, wherein, inresponse to receiving the request for signature, the issuer device isconfigured to compute an issuer signature by signing both the user'strusted identity and the user public key using an issuer private keyallocated to the issuer, wherein the issuer device is configured togenerate a hash of the trusted identity, wherein the issuer device isconfigured to send the trusted identity to the user device, and whereinthe issuer device is configured to create a block chain transactioncontaining the hash and to submit the block chain transaction to a BlockChain for transaction verification and storage to the block chainaddress.